1. Field of the Disclosure
The present disclosure relates generally to electrophotographic image forming devices and more particularly to a bi-directional spring brake for a photoconductive drum of an electrophotographic image forming device.
2. Description of the Related Art
As is well known in the art, during a print operation by an electrophotographic image forming device a charge roll charges the surface of a photoconductive drum to a predetermined voltage. The charged surface of the photoconductive drum is then selectively exposed to a laser light source to selectively discharge the surface of the photoconductive drum and form an electrostatic latent image on the photoconductive drurnm corresponding to the image being printed. Toner is picked up by the latent image on the photoconductive drum from a developer roll creating a toned image on the surface of the photoconductive drum. The toned image is then transferred from the photoconductive drum to the print media either directly by the photoconductive drum or indirectly by an intermediate transfer member. A cleaning blade or roller removes any residual toner adhering to the photoconductive drum after the toner is transferred from the photoconductive drum. The cleaned surface of the photoconductive drum is then ready to be charged again and exposed to the laser light source to continue the printing cycle.
The photoconductive drum may include a spring brake that applies a uniform drag on the photoconductive drum when the photoconductive drum rotates in an operative rotational direction in order to minimize jitter and backlash of the photoconductive drum. FIG. 1 shows a prior art photoconductive drum 20. Photoconductive drum 20 includes a hollow cylindrical drum member 22 having an outer surface 24. Drum member 22 is mounted on a shaft 26 that defines a rotational axis 28 of photoconductive drum 20. An end cap 30 is positioned on an axial end 32 of drum member 22. End cap 30 includes a circular hub 34 on an outboard side of end cap 30. Hub 34 has an opening 36 that is centered around rotational axis 28. Shaft 26 is attached to end cap 30 and passes through opening 36 such that shaft 26, end cap 30 and drum member 22 rotate in unison.
With reference to FIGS. 1 and 2, photoconductive drum 20 includes a spring brake 40 mounted on end cap 30. Spring brake 40 includes a segment of spring wire 41 that forms a coiled portion 42 and a pair of arms 44, 46. Coiled portion 42 includes a middle portion of spring wire 41 coiled around a center axis 43. Arms 44, 46 are formed by respective ends of spring wire 41. Coiled portion 42 is wrapped around hub 34 of end cap 30. Arm 44 extends beyond an outer circumference of end cap 30 and is positioned to contact a stop 48 (shown schematically) when photoconductive drum 20 rotates in an operative rotational direction indicated by arrow A in FIG. 1. When photoconductive drum 20 rotates in the operative rotational direction, spring brake 40 rotates with end cap 30 until arm 44 contacts stop 48, which stops the rotation of spring brake 40 with photoconductive drum 20. When arm 44 contacts stop 48, the force on arm 44 from stop 48 causes arm 44 to flex counter to the operative rotational direction of photoconductive drum 20 which, in turn, causes coiled portion 42 to unwind slightly from hub 34. Coiled portion 42 remains in contact with hub 34 but allows photoconductive drum 20 to continue rotating with coiled portion 42 applying a uniform drag on photoconductive drum 20. Arm 46 is spaced clear of arm 44 and provides no functionality other than forming an end of spring brake 40.